This invention relates to apparatus for securing a wheel member of a turbo-machine to a rotatable shaft, and in particular to an arrangement which positively secures the wheel to the shaft without generating torsional forces.
Rotors of turbo-machinery, such as centrifugal compressors, radial turbines, and axial compressors and turbines, are at times manufactured as a composite structure, wherein the disks or wheels of a turbo-machine are attached to stub shafts, which are fixed to the end of a thru-bolt, sometimes referred to as a tie-bolt. In achieving the composite structure, heat has been applied to the thru-bolts for developing forces to positively secure the disks to the shafts. In order to apply the heat, holes have been drilled through the entire length of the shafts, destroying the integrity of the shafts and increasing the problems associated with achieving a dynamic and static balance of the rotor. In addition, alignment of the shaft has been difficult to achieve without complicated and relatively expensive manufacturing techniques. It has been suggested that the heating step used to positively secure the disks to the shaft be eliminated, and that compression and torsional forces developed through the use of appropriate stud and nut arrangements be used to achieve the desired mating of the wheel and shaft.
However, turbo-machinery employed in many applications such as power recovery installations, operate at relatively high temperatures. Thus, the working strength of the various elements of the turbo-machine are reduced as the working strength of a metallic component generally varies inversely to the temperature of the environment in which the component operates. The torsional forces develop in securing the wheel to the shaft will generate torsional stresses. Such stresses may result in the failure of one or more of the studs due to the relatively low value of the working strength of the studs. As in obvious, failure of a connecting stud may result in major damage to the turbo-machine.